In a Voice over LTE (VoLTE) call, voice service is provided as a data flow over a Long-Term Evolution (LTE) data bearer. During set up of a VoLTE call, the two user equipment (UE) device endpoints exchange capabilities in a negotiation mediated by an IP Multimedia Core Network Subsystem (IMS). In particular, the UEs exchange information regarding the codec and rates that they support, such as the AMR-WB (Adaptive Multi Rate Wide Band) codec rates that they support. AMR-WB is a speech audio coding standard that is codified as G.722.2, an ITU-T standard. AMR-WB operates on nine different bit rate modes, and in a typical call set-up, the UE devices exchange their bit rate modes and select the highest bit rate supported by both.
VoLTE utilizes Real-time Transport Protocol (RTP), which provides for voice (and video) transmission over Internet Protocol (IP) networks. RTP provides mechanisms for jitter compensation and detection of out-of-order arrival of data. Real-time control Protocol (RTCP) is used to exchange information regarding an RTP session.